1. Field of the Invention
The present invention relates generally to a beam projector, and more particularly to a focusing device for an ultra-compact beam projector that is mountable on a compact appliance, such as a portable terminal.
2. Description of the Related Art
A beam projector is a device which includes a light source, one or more Liquid Crystal Display (LCD) panels, one or more lenses, or the like, wherein light projected from the light source is transmitted through the LCD panels to project an image displayed on the LCD panels onto a screen. The number of the LCD panels and the number of the lenses may vary according to the type of beam projector.
The beam projector may be used to display an image which is larger than possible on the compact appliance. As a result, the beam projector is useful in conferences, presentations or the like. Portable terminals equipped with ultra-compact beam projectors have recently become commercially available. Such portable terminals equipped with a beam projector are useful to businesses who frequently make business trips or attend conferences.
A beam projector that is designed to be mounted on a compact appliance, such as a portable terminal, is generally provided with a focusing device employing a control knob, such as a dial.
Focusing devices provided in conventional projectors may convert rotary movement of a control knob into rectilinear movement of a lens holder through a rack and pinion gear, or through a connecting rod.
Using a rack and pinion gear has an advantage in that a user's manipulation may be precisely transmitted so as to move the lens holder forward or backward. However, if the user applies excessive force when the lens holder has arrived at the end of the available space, the teeth of the rack and pinion gear may be damaged. Moreover, a rack and pinion gear is provided in a compact portable terminal are often damaged when the portable terminal is dropped.
Using a connecting rod has an advantage in that the possibility of damaging the connecting rod is relatively low. However, there is a disadvantage in that since the moving space of the connecting rod is maintained in an opened state, internal structures, such as the lens holder, are exposed to an external environment. Therefore, it is difficult to produce a high-quality focusing device or a beam projector itself. In such designs, the focusing device or the beam projector is vulnerable to external risks, such as water permeation. Moreover, since the connecting rod should be arranged in relation to the moving path of the lens holder, it must be sufficiently long, which is an obstacle to reduce the size of such a beam projector.